Polyamide resins have excellent characteristics such as an excellent mechanical characteristic and thermal characteristic, and are therefore widely used as materials for various molded articles such as fibers, various containers, films, electric and electronic components, automobile components and machine components.
In recent years, demands for miniaturization, complication, thinning and weight reduction of molded articles have been increased, and development of a material excellent in molding processability and excellent in mechanical characteristic is required. In addition, from the viewpoint of lowering a molding processing temperature and shortening a molding cycle, improvement of molding processability that contributes to reduction of environmental loading and reduction of energy costs is required. In general, an increase in molecular weight of a polyamide resin is known to improve the mechanical characteristic of the polyamide resin, but also has the effect of reducing the melt fluidity of the polyamide resin, resulting in deterioration of molding processability. When the molding processing temperature is increased, melt fluidity can be improved, but there is the problem that the mechanical characteristic and the appearance of a molded article are deteriorated because thermal stability is deteriorated, leading to occurrence of thermal decomposition that causes molecular weight reduction and gas generation during molding processing.
As a method for improving the thermal stability of a polyamide resin, for example, a method has been suggested in which thermal decomposition from the end of the polyamide resin is suppressed by blocking the amino end group and the carboxyl end group of the polyamide resin using acetic acid and diazomethane, respectively (see, for example, Non-Patent Document 1). By such a technique, thermal stability can be improved to increase the molding processing temperature, but there is the problem that the melt viscosity is still high, and molding processability is insufficient in view of demands for miniaturization, complication, thinning and weight reduction of molded articles in recent years.
In addition, as a polyamide resin excellent in mechanical properties and fluidity, a polyamide resin which contains a hydrocarbon group having 6 to 22 carbon atoms and has a relative viscosity of 2 or more and less than 2.5 has been suggested (see, for example, Patent Document 1). However, there is the problem that such a polyamide resin still has a high melt viscosity, and insufficient molding processability in view of demands for miniaturization, complication, thinning and weight reduction of molded articles in recent years. On the other hand, as a high-molecular-weight end modified polyamide resin having excellent molding processability and excellent crystallinity, an end modified polyamide resin containing 0.5 to 4.5% by mass of a specific end structure and having a relative viscosity ηr of 2.1 to 10 has been suggested (see, for example, Patent Document 2).